Brain and central nervous system (CNS) tumors are a diverse group of cancers that arise in the brain, meninges, spinal cord, and other parts of the CNS. They may be classified as benign or malignant, and may be primary in origin or metastatic.
Gliomas are one of the most frequent types of nervous system tumors. Gliomas comprise nearly half of all primary brain tumours and a fifth of all primary spinal cord tumours. Gliomas are tumours of the glial cells most often astrocytes; these cells support and protect nerve cells in the brain. Gliomas may occur anywhere in the brain or spinal cord, including the cerebellum, brain stem, or optic chiasm. Gliomas often carry a poor prognosis and thus are among the most devastating diseases. Of all brain tumors diagnosed each year, about half are malignant gliomas and result in death within 18 months.
Gliomas can be divided into two groups based on their growth characteristics: low-grade gliomas and high-grade gliomas. Low-grade gliomas are usually localized and grow slowly over a long period of time. Examples of low-grade gliomas include astrocytomas, oligodendrogliomas, pilocytic astrocytomas. Over time, most of these low-grade gliomas dedifferentiate into more malignant high-grade gliomas that grow rapidly and can easily spread through the brain. Examples of high-grade gliomas include anaplastic astrocytoma and glioblastoma multiforme.
Glioblastoma multiforme (GBM), also known as spongioblastoma multiforme, is the most common of these, accounting for 45.2% of all malignant brain and CNS cancers (Ostrom et al., 2014 The epidemiology of glioma in adults: a “state of the science” review. Neuro-Oncology, 16(4), 896-913). The annual incidence of GBM varies from 5 to 7 per 100,000: each year, about 25,000 new cases are diagnosed in the European Union and about the same number in the United States. Signs and symptoms depend on several factors (size, rate of growth, localization of the tumor) and are mainly represented by headaches, seizures, neurological deficits, and changes in mental status.
The treatment for gliomas generally involves surgical removal, followed by a course of radiation and chemotherapy. As for current chemotherapy, temozolomide, an oral methylating chemotherapeutic agent, became the standard of care for newly diagnosed GBM, when used concurrently with external beam radiation followed by adjuvant therapy. In patients with newly diagnosed GBM, current standard treatments provide median overall survival of a little over one year. In patients with relapsed or progressive GBM, the prognosis is particularly poor. Almost all patients with GBM die within five years.
Temozolomide (TMZ) (brand names Temodar and Temodal and Temcad) also known as 3,4-dihydro-3-methyl-4-oxoimidazo [5,1-d]-as-tetazine-8-carboxamide (see U.S. Pat. No. 5,260,291), is an oral chemotherapy drug used in glioma therapy, with little to no success. It is an alkylating agent used for the treatment of GBM—as well as for treating melanoma, a form of skin cancer. Temozolomide is also indicated for relapsed Grade III anaplastic astrocytoma. Temozolomide is a prodrug and an imidazotetrazine derivative of the alkylating agent dacarbazine. The therapeutic benefit of temozolomide depends on its ability to alkylate/methylate DNA, which most often occurs at the N-7 or 0-6 positions of guanine residues. This methylation damages the DNA and triggers the death of tumor cells. However, some tumor cells are able to repair this type of DNA damage, and therefore diminish the therapeutic efficacy of temozolomide, by expressing a protein O6-alkylguanine DNA alkyltransferase (AGT) encoded in humans by the O-6-methylguanine-DNA methyltransferase (MGMT) gene. In some tumors, epigenetic silencing of the MGMT gene prevents the synthesis of this enzyme, and as a consequence such tumors are more sensitive to killing by temozolomide. Conversely, the presence of AGT protein in brain tumors predicts poor response to temozolomide and these patients receive little benefit from chemotherapy with temozolomide.
Even with the combination of radiotherapy plus temozolomide, median survival was 14.6 months at a median follow-up of 28 months (Stupp et al., New England J. Med., 352:987 (2005)). The two-year survival rate was 26.5 percent with radiotherapy plus temozolomide and 10.4 percent with radiotherapy alone.
Therefore, in spite of the introduction of temozolomide, further research for the development of new agents active against glioma is warranted in order to prevent drug resistance. Indeed, there is still an unmet medical need for new potent agents for the treatment of gliomas. The present invention is directed to meeting this and other needs.
The present inventors have discovered that the compound 2-(2,6-dichlorobenzylidene)hydrazinecarboximidamide, also referred to as guanabenz, and various guanabenz derivatives disclosed herein, when used in combination with conventional chemotherapeutic agents, such as temozolomide, provide synergistic anti-tumor responses in an in vivo model of glioma compared to conventional chemotherapeutic agents such as temozolomide when used alone.
Guanabenz:
is an alpha agonist of the alpha-2 type that was used as an antihypertensive drug. In addition, guanabenz and some guanabenz derivatives protect cells from otherwise lethal accumulation of misfolded proteins in the endoplasmic reticulum (ER), a phenomenon called ER stress which activates the Unfolded Protein Response (UPR) which meticulously coordinate adaptive and apoptotic responses to ER stress. Guanabenz and some guanabenz derivatives are acting by binding to a regulatory subunit of protein phosphatase 1, PPP1R15A (GADD34), selectively disrupting the stress-induced dephosphorylation of the α subunit of translation initiation factor 2 (eIF2α). Thus, guanabenz and some guanabenz derivatives set the translation rates in stressed cells to a level manageable by available chaperones, thereby restoring protein homeostasis. It was reported that guanabenz does not bind to the constitutive PPP1R15B (CReP) and therefore does not inhibit translation in non-stressed cells (Tsaytler et al., 2011 Science 332 pp 91-94; Das et al., 2015 Science 348 pp 239-242).
ER stress is present in cancer cells; indeed following initiation of malignancy, rapid tumour growth and inadequate vascularization result in micro-environmental stress which activates the UPR. Enhanced ER stress signalling and increased chaperone expression is linked to drug resistance and constitutes an adaptive capacity of cancer cells to maintain ER protein homeostasis (or proteostasis), thereby counteracting apoptosis (Yadav et al. 2014 J. Cancer Prevention 19 pp 75-88; Lee et al. 2008 Neuro-oncology 10 pp 236-243). The UPR, when coupled with induced tumour dormancy, dually protects neoplastic cells from apoptosis and permits recurrence once favourable growth conditions have been restored. However, if ER stress is prolonged and the UPR fails to restore ER proteostasis, tumour cell apoptosis ensues (Vandewynckel et al. 2013 Anticancer Res. 33 pp 4683-4694).
Thus, cancer treatments with chemotherapeutic agent and PPP1R15A inhibitors to restore protein homeostasis have been proposed:
EP2059233 discloses the use of PPP1R15A inhibitor in combination with a second product used in cancer treatment, such as etoposide or mitomycin C, to prepare a pharmaceutical composition to prevent or treat cancer in mammals.
WO2010/054381 discloses the use of non-selective PPP1R15A inhibitor, salubrinal, in combination with a proteasome inhibitor such as bortezomib to prepare a pharmaceutical composition to prevent or treat cancer in mammals;
WO 2008/061647 (Acure Pharma AB) discloses the use of N-(2-chloro-3,4-dimethoxybenzylideneamino)guanidine as a VEGFR inhibitor and its associated applications in the treatment or prevention of undesired blood vessel formation during tumour growth.
US2014/0235556 discloses methods and combination of temozolomide and various marketed drugs to treat gliomas. Moreover, US2014/0235556 shows that the combination of temozolomide and intraperitoneally administered guanabenz has no anti-tumor effect in a rodent model of gliomas.
Unexpectedly, the present inventors have now discovered that guanabenz and various guanabenz derivatives disclosed herein, when used in combination temozolomide, provide synergistic anti-tumor responses in an in vivo model of glioma. These findings offer a new approach to the treatment of cancer, particularly gliomas, and more particularly glioblastomas.